1. Field of Invention
The invention relates to a thin film magnetic head having at least an inductive magnetic transducer for writing, and a method of manufacturing the same.
2. Description of Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a stacked structure comprising a recording head having an inductive magnetic transducer for writing and a reproducing head having a magnetoresistive (hereinafter referred to as MR) element for reading, is widely used as the thin film magnetic head.
To increase a recording density of the performance of the recording head, it is necessary to increase a track density on a magnetic recording medium. For this purpose, it is necessary to realize a recording head having a narrow track structure in which a top pole and a bottom pole, which are formed on and under a write gap therebetween, respectively, have a narrow width that is from a few microns to the submicron order on an air bearing surface, and semiconductor fabrication technology is used in order to achieve the above-mentioned recording head.
The description is now given with reference to FIGS. 29 to 34 with regard to a method of manufacturing a composite thin film magnetic head as an example of a method of manufacturing a thin film magnetic head of the related art.
In the manufacturing method, first of all, as shown in FIG. 29, an insulating layer 102 made of, for example, aluminum oxide (Al2O3, hereinafter referred to as “alumina”) is deposited with a thickness of about 5.0 μm to 10.0 μm on a substrate 101 made of, for example, altic (Al2O3—TiC). Then, a bottom shield layer 103 for a reproducing head is formed on the insulating layer 102. Then, an alumina layer, for example, is deposited with a thickness of 100 nm to 200 nm on the bottom shield layer 103 by means of sputtering, and thus a shield gap film 104 is formed. Then, an MR film 105 for constituting an MR element for reproducing is formed with a thickness of a few tens of nanometers on the shield gap film 104 in such a manner that the MR film 105 has a desired pattern by means of high-accuracy photolithography. Then, lead layers (riot shown) for functioning as lead electrode layers to be electrically connected to the MR film 105 are formed on both sides of the MR film 105. After that, a shield gap film 106 is formed on the lead layers, the shield gap film 104 and the MR film 105, and thus the MR film 105 is sandwiched in between the shield gap films 104 and 106. Then, a top shield-cum-bottom pole (hereinafter referred to as “a bottom pole”) 107 made of a magnetic material for use in both the reproducing and recording heads, e.g., a nickel-iron alloy (NiFe, hereinafter referred to as “Permalloy (a trade name)”) is formed on the shield gap film 106.
Then, as shown in FIG. 30, a write gap layer 108 made of an insulating material, e.g., alumina is formed on the bottom pole 107. Then, a photoresist film 109 is formed into a predetermined pattern on the write gap layer 108 by means of high-accuracy photolithography. Then, a thin film coil 110 made of, for example, copper (Cu) for an inductive recording head is formed on the photoresist film 109 by means of electroplating. Then, a photoresist is formed into a predetermined pattern by means of high-accuracy photolithography so as to coat the photoresist film 109 and the thin film coil 110, and thereafter the photoresist is subjected to heat treatment at a temperature of 250 degrees, for example. By this heat treatment, a photoresist film 111 for providing insulation between windings of the thin film coil 110 is formed.
Then, as shown in FIG. 31, a part of the write gap layer 108, which is located rearward with respect to the thin film coil 110 (on the right side in FIG. 31), is etched in order to form a magnetic path, whereby an opening 108a is formed and thus the bottom pole 107 is partly exposed. Then, a top yoke-cum-top pole (hereinafter referred to as “a top pole”) 112 made of a magnetic material for the recording head, e.g., Permalloy is formed by means of electroplating so as to coat an exposed surface of the bottom pole 107, the photoresist film 11 and the write gap layer 108. For example, the top pole 112 has a planar shape shown in FIG. 34 to be described later and includes a yoke portion 112a and a pole chip portion 112b. The top pole 112 is in contact with and magnetically coupled to the bottom pole 107 in the opening 108a. Then, the respective parts of the write gap layer 108 and the bottom pole 107, which are located in a peripheral region around the pole chip portion 112b, are selectively etched and removed by about 0.5 μm by means of ion milling using the pole chip portion 112b of the top pole 112 as a mask (see FIG. 33). Then, an overcoat layer 113 made of, for example, alumina is formed so as to coat the top pole 112. Finally, a track surface of the recording head and the reproducing head, i.e., an air bearing surface 120 is formed through the steps of machining and polishing, and thus a thin film magnetic head is completed.
FIGS. 32 to 34 show a structure of the completed thin film magnetic head. FIG. 32 shows a cross section of the thin film magnetic head in a direction perpendicular to the air bearing surface 120. FIG. 33 shows an enlarged view of a cross section of a pole portion 500 in a direction parallel to the air bearing surface 120. FIG. 34 shows a planar structure of the thin film magnetic head. FIG. 31 corresponds to a cross section viewed in the direction of the arrows along the line XXXI—XXXI of FIG. 34. FIGS. 32 to 34 do not show the overcoat layer 113 and so forth. FIG. 34 shows the thin film coil 110 and the photoresist film 111 whose outermost ends alone are shown.
In FIGS. 32 and 34, “TH” indicates a throat height, and “MRH” indicates an MR height. The “throat height (TH)” refers to one of factors that determine the performance of the recording head, and refers to a length between the position of an edge of an insulating layer (the photoresist film 111) for electrically isolating the thin film coil 110 from the other conductive portions, which is closest to the air bearing surface 120, i.e., a throat height zero position (a TH0 position), and the position of the air bearing surface 120. An optimization of the throat height (TH) is desired for an improvement in the performance of the recording head. The throat height (TH) is controlled by the amount of polishing of the air bearing surface 120. The “MR height (MRH)” refers to a length between the position of a farthest edge of the MR film 105 from the air bearing surface 120, i.e., an MR height zero position (an MRH0 position), and the position of the air bearing surface 120. The MR height (MRH) is also controlled by the amount of polishing of the air bearing surface 120.
Factors that determine the performance of the thin film magnetic head include an apex angle (θ) shown in FIG. 32, as well as the throat height (TH), the MR height (MRH) and so on. The apex angle θ refers to an average degree of inclination of an inclined surface of the photoresist film 111 close to the air bearing surface 120.
As shown in FIG. 33, a structure in which the respective parts of the write gap layer 108 and the bottom pole 107 are etched in self-alignment with the pole chip portion 112b of the top pole 112 is called a trim structure. The trim structure allows preventing an increase in an effective track width resulting from a spread of a magnetic flux generated during the writing of data on a narrow track. “P2W” indicates a width of a portion (hereinafter referred to as “a pole portion 500”) having the trim structure, namely, a pole width (or “a track width”). “P2L” indicates a thickness of the pole chip portion 112b constituting a part of the pole portion 500, namely, a pole length. Lead layers 121 for functioning as lead electrode layers to be electrically connected to the MR film 105 are provided on both sides of the MR film 105. The lead layers 121 are not shown in FIGS. 29 to 32.
As shown in FIG. 34, the top pole 112 has the yoke portion 112a occupying most of the top pole 112, and the pole chip portion 112b having a substantially uniform width as the pole width P2W. An outer edge of the yoke portion 112a forms an angle α with a surface parallel to the air bearing surface 120 in a coupling portion between the yoke portion 112a and the pole chip portion 112b. An outer edge of the pole chip portion 112b forms an angle β with the surface parallel to the air bearing surface 120 in the above-mentioned coupling portion. FIG. 34 shows the case where α and β are, for example, about 45 degrees and about 90 degrees, respectively. As described above, the pole chip portion 112b is a portion for functioning as a mask for forming the pole portion 500 having the trim structure. As can be seen from FIGS. 32 and 34, the pole chip portion 112b lies on the flat write gap layer 108, and the yoke portion 112a lies on a coil portion (hereinafter referred to as “an apex portion”), which is coated with the photoresist film 111 and rises like a hill.
Detailed structural features of the top pole are described in Unexamined Japanese Patent Application Publication No. Hei 8-249614, for example. The publication gives the description with regard to the top pole having a structure in which a width of a portion located rearward with respect to the TH0 position (that is, located away from the air bearing surface 120) becomes gradually greater.
In the thin film magnetic head shown in FIGS. 31 and 34, when a current passes through the thin film coil 110 at the time of the recording operation of information, a magnetic flux is generated in response to the current. The generated magnetic flux propagates through the top pole 112 from the yoke portion 112a to the pole chip portion 112b, and further propagates and reaches to a tip portion of the pole chip portion 112b close to the air bearing surface 120. After reaching to the tip portion of the pole chip portion 112b, the magnetic flux generates a signal magnetic field for recording to the outside near the write gap layer 108. The signal magnetic field partly magnetizes a magnetic recording medium, thereby enabling information to be recorded on the magnetic recording medium.
The pole width P2W of the pole portion 500 determines a write track width on the magnetic recording medium. To increase the recording density, it is necessary that the pole portion 500 be formed with high accuracy so as to make the pole width P2W extremely small. Too great a pole width P2W causes a phenomenon in which data is written on adjacent regions as well as a predetermined write track region on the magnetic recording medium, namely, a side erase phenomenon, which therefore makes it impossible to increase the recording density. In recent years in particular, it has been required that the pole width P2W be locally minimized to about 0.3 μm or less in order to enable recording at a high surface recording density, that is, in order to form a recording head having a narrow track structure, and therefore an urgent necessity is to establish manufacturing technology for locally minimizing the pole width P2W.
Frame plating is used as a method of forming the top pole, as described in Unexamined Japanese Patent Publication No. Hei 7-262519, for example. The top pole 112 is formed by use of frame plating in the following manner. First, a thin electrode film made of, for example, Permalloy is formed over an underlayer including the apex portion by means of sputtering, for instance. Then, the electrode film is coated with a photoresist so as to form a photoresist film, thereafter the photoresist film is patterned by means of photolithography, and thus a frame pattern (an outer frame) for plating is formed. The frame pattern has an opening pattern corresponding to the planar shape of the top pole 112. Then, the top pole 112 made of, for example, Permalloy is formed in the opening pattern of the frame pattern by means of electroplating using the frame pattern as a mask and using as a seed layer the electrode film formed in the preceding step.
The apex portion is located higher than the other portions by 7 to 10 μm or more, for example. The apex portion is coated with a photoresist of 3 mm to 4 μm in thickness. When a film thickness of the photoresist on the apex portion must be at least 3 μm or more, a photoresist film having a thickness of, for example, 8 to 10 μm or more is formed under the apex portion because the fluidic photoresist flows intensively to a lower place.
To realize the locally minimum pole width P2W, it is necessary to form the frame pattern having the opening pattern having a locally minimum width (e.g., 1.0 μm or less) corresponding to the pole width P2W. That is, the opening pattern having a locally minimum width of 1.0 μm or less must be formed by the photoresist film having a thickness of 8 to 10 μm or more. However, it is very difficult in manufacturing process to form the frame pattern having the opening pattern having the locally minimum width by using the above-mentioned photoresist film having a great film thickness.
In the case where the top pole 112 is formed on a region having an uneven structure comprising the apex portion and so on, there is, moreover, a problem that the accuracy in forming the top pole 112 deteriorates greatly for the following reason. That is, when the photoresist film formed on the region having the uneven structure is subjected to exposure in the step of forming the frame pattern for forming the top pole 112, light is reflected obliquely or transversely from an inclined surface portion or the like of the underlayer (the electrode film). The reflected light causes an increase or a reduction in an exposed region in the photoresist film. Consequently, in the photoresist film, the width of the opening pattern having the locally minimum width corresponding to the pole chip portion 112b of the top pole 112 increases in a width direction.
Besides the above-mentioned problem about the accuracy in forming the top pole 112, a problem exists: that is, overwrite characteristics of the thin film magnetic head deteriorate for the following reason. That is, when the pole width P2W is locally minimized, a magnetic volume of the pole chip portion 112b constituting the pole portion 500 generally becomes lower. The “magnetic volume” refers to the capacity of magnetic flux that can be contained in a magnetic layer portion. When the pole width P2W becomes smaller and thus the “magnetic volume” of the pole chip portion 112b is not properly ensured, “saturation of magnetic flux” occurs in the pole chip portion 112b, so that the magnetic flux cannot sufficiently reach to the tip portion of the pole chip portion 112b. In particular, when a magnetic material such as Permalloy having a magnetic flux density of about 1.2 tesla is used as a material of the top pole 112, processing characteristics for forming a desired magnetic layer pattern become facilitated, but, when the pole width P2W is locally minimized (to about 0.3 μ□m or less), the magnetic flux is saturated in the pole chip portion 112b, so that the magnetic flux is insufficiently supplied to the tip portion of the pole chip portion 112b. 